1. Field of the Invention
This invention relates to a safety indicator for use with safety cables, and more particularly to a shock load indicator for use with retracting life line devices
2. Description of Related Art
Fall protection of workers, particularly in industrial environments, is accomplished with safety harnesses worn by the worker attached to a secure point through a lifeline, usually a steel cable or synthetic line.
Because the shock forces produced on an arresting line as a result of a human body falling even as small a distance as 6 ft. are quite, it is known practice to provide the lifeline with some form of retracting and/or frictional braking mechanism to limit the extend of free fall and the shock load to the line as the fall is arrested. A typical such system of line retraction and brake is sold by R.T.C. located in Wilmington Del., under the trademark RETRACTALOK.RTM.. Certain models are equipped with an indicator button which shows whether the unit has been used to arrest a fall so that it may be returned to the manufacturer for recertification. This button is spring loaded and is pushed outwardly by a lever when the arrestor operates to break a fall.
When a cable or rope lifeline is subjected to shock load, as from arresting a fall, it should be replaced since the load weakens the cable or rope making it unsafe for further use as a lifeline.
U.S. Pat. No. 5,090,503 shows a device which provides the frictional breaking action together with an indicator which shows whether the life line has been used to prevent a fall. This device is primarily for use on life lines comprised of rope rather than cable, and requires that the rope be folded over and clamped together; this arrangement provides the frictional force used to counteract the force due to the falling weight. However such folding over results in sharp bending and is not recommended for cables.
U.S. Pat. No. 5,143,187 shows an energy absorber and fall protection system which may be placed between a lifeline and its point of attachment. This device employs a series of breaking links which as they break allow a folded section of a chain interposed between the lifeline and the point of attachment thereof to extend, simultaneously cushioning the fall by absorbing energy and indicating by the chain elongation that a fall has occurred.
U.S. Pat. No. 5,220,977 also shows a fall indicator for use with life lines. As with the previous device, this indicator must also be placed between the lifeline and its attachment point to the person using such line, or between the lifeline and the anchoring point thereof. The structures shown in the above references are complex and relatively expensive. Interposing the indicators between the life line and its the point of attachment, introduces additional attachment points which are potential weak links any one of which may fail.
There is still need in the industry for a shock indicator which may be used on a lifeline, cable or rope, without weakening or otherwise compromising the holding power of the cable or rope itself, and which will reliably indicate whether the cable or rope has been subjected to shock loading as from a fall. The term cable will be used hereinafter in this descriprtion to indicate both rope and cable safety or life lines.
These and other objects of the present invention will be clear from the following description.